(Upper Cambrian, Paibian) Trilobite Faunule in the Central Conasauga River Valley, North Georgia, Usa

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SOUTHEASTERN GEOLOGY V. 49, No. 1, June 2012, p. 31-41

AN APHELASPIS ZONE (UPPER CAMBRIAN, PAIBIAN) TRILOBITE FAUNULE IN THE CENTRAL CONASAUGA RIVER VALLEY, NORTH GEORGIA, USA

DAVID R. SCHWIMMER1

WILLIAM M. MONTANTE2 1Department of Chemistry & Geology Columbus State University, 4225 University Avenue, Columbus, Georgia 31907, USA 2Marsh & McLennan, Inc., 3560 Lenox Road, Suite 2400, Atlanta, Georgia 30326, USA

ABSTRACT shelf-to-basin break, which is interpreted to be east of the Alabama Promontory and in Middle and Upper Cambrian strata the Tennessee Embayment. The preserva- (Cambrian Series 3 and Furongian) in the tion of abundant aphelaspine specimens by southernmost Appalachians (Tennessee to bioimmuration events may have been the re- Alabama) comprise the Conasauga Forma- sult of mudflows down the shelf-to-basin tion or Group. Heretofore, the youngest re- slope. ported Conasauga beds in the Valley and Ridge Province of Georgia were of the late INTRODUCTION Middle Cambrian (Series 3: Drumian) Bo- laspidella Zone, located on the western state Trilobites and associated biota from Middle boundary in the valley of the Coosa River. Cambrian beds of the Conasauga Formation in Two new localities sited eastward in the Co- northwestern Georgia have been described by nasauga River Valley, yield a diagnostic suite Walcott, 1916a, 1916b; Butts, 1926; Resser, of trilobites from the Upper Cambrian 1938; Palmer, 1962; Schwimmer, 1989; Aphelaspis Zone. Very abundant, Schwimmer and Montante, 2007. These fossils polymeroid trilobites at the primary locality and deposits come from exposures within the are referable to Aphelaspis brachyphasis, valley of the Coosa River, in Floyd County, which is a species known previously in west- Georgia, and adjoining Cherokee County, Ala- ern North America. A second locality has bama. Trilobite biozone associations of these produced a few identifiable specimens of the Middle Cambrian biotas are of the Glyphaspis aphelaspine Eugonocare (Olenaspella) sepa- to Crepicephalus Zones of the traditional Lau- ratum. Specimens at these two localities are rentian Middle Cambrian Series. generally complete individuals compressed Cambrian trilobites have not been described in tan mudstones. The primary locality fea- farther east- or southward from the above in the tures abundant body cluster accumulations, southern Appalachian outcrop, although the implying mass mortality by bioimmuration. Conasauga Formation is exposed in a separate The trilobite assemblage also includes the ag- fault-bounded slice in the Conasauga River Val- nostoids Glyptagnostus reticulatus, Agnostus ley (Figure 1). We report here new Upper Cam- inexpectans, and Aspidagnostus rugosus, all brian localities in this outcrop, containing the correlated to the global Paibian agnostoid southeastern-most Cambrian trilobites in North Glyptagnostus reticulatus Zone. These locali- America. The new trilobite assemblages in- ties contain the southeastern-most Late clude polymeroids of the Laurentian Upper Cambrian faunule in the Appalachians. The Cambrian Aphelaspis Zone, including Aphelas- trilobite species and carbonate-free, mud- pis brachyphasis and Eugonocare (Ole- stone lithology, lacking evidence of infaunal naspella) separatum; and coeval agnostoids of bioturbation and burrowing, suggest accu- the global Glyptagnostus reticulatus Zone, in- mulation eastward of a paleotopographic cluding Glyptagnostus reticulatus, Agnostus in-

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Figure 1a— Map of Conasauga Formation Figure 1b—correlation chart showing the outcrops in Georgia with Aphelaspis Zone stratigraphic position of the Aphelaspis localities in the Conasauga River Valley faunule. (Correlation chart based on Bab- indicated, also showing the general geo- cock and Peng, 2007, and Ogg, 2009). graphic position of the trilobite beds (discussed in text) in the proximal Coosa River Valley.

expectans, and Aspidagnostus rugosus. in the southern Appalachians, the occurrence of In contrast with most prior reports of Upper a well-demarcated Aphelaspis assemblage with Cambrian trilobites from the Southern Appala- the globally-correlative agnostoid Glyptagnos- chians (e.g. Butts, 1926; Resser, 1938; Palmer, tus reticulatus Zone provides well-dated Upper 1962; Rasetti, 1965), specimens collected in the Cambrian sites in the south-easternmost Appa- new localities are preserved in mudstones as lachians. compressed, typically complete individuals, with intact librigenae. At Locality 1 (Figure 1a), GEOLOGIC SETTING Aphelaspis specimens are very abundant, with intact librigenae, associated in “body clusters” The localities here are in the Conasauga For- (sensu Whittington, 1997b), and commonly mation in Murray and Gordon Counties, north- surrounded by decay-gas induced iron oxide ha- western Georgia. This study area (Figure 1a) is los (Schwimmer and Montante, 2007). These in the Appalachian Valley and Ridge Province, new trilobite localities contain relatively few characterized by series of northeast-trending, agnostoids, but enough species are present (as ridge-forming Paleozoic thrust faults and trans- indicated above) to be clearly referable within forms, with relatively low valleys floored with the global Cambrian agnostoid-based stratotype less-resistant strata sandwiched between fault system (Peng and Robison, 2000; Babcock and boundaries. The mudstones of the Conasauga others, 2007; and see discussion in “Biostratig- Formation form two such valleys (Figure 1a), raphy”). In addition to extending the southeast- and the two localities discussed here lie in the ern geographic range of Upper Cambrian strata broad valley of the Conasauga River, situated

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between the East Coosa and Cartersville Faults BIOSTRATIGRAPHY (Thomas and others, 2000; Thomas and Bayo- na, 2005). Locality 1 is a riverside outcrop on Trilobites from both new localities are as- the Conasauga River in Murray County, in the signed to the Aphelaspis Zone (Figure 1b), vicinity of Chatsworth, Georgia, on the eastern which is coeval with the lowermost biozone of side of the Conasauga River Valley. This local- the global of the Furongian Series (= Upper ity has an approximately 4.0 meter-thick expo- Cambrian in traditional Laurentian nomencla- sure of abundantly fossiliferous, tan-to-olive, ture: Ludvigsen and Westrop, 1985). The Con- flaggy-bedded mudstones exposed on the banks asauga sites in consideration are assigned to the of the river and in ancillary drainages. Aphelaspis Zone based on the co-occurrence of Polymeroid trilobites are very abundant at this Aphelaspis brachyphasis, and Eugonocare site, and include numerous individuals with at- (Olenaspella) separatum (Palmer, 1962, 1965; tached librigenae. Locality 2, which is now cov- Pratt, 1992). ered, was a commercial borrow-pit excavation The base of the Aphelaspis Biozone is bio- in the vicinity of Calhoun, Georgia, in southern- stratigraphically equivalent to the first appear- most Gordon County, exposing approximately ance of the agnostoid Glyptagnostus reticulatus 6.0 m of olive-green mudstones with a relative- (Babcock and others, 2005). This species is the ly sparse trilobite fauna. This locality is in the eponym of the biozone that comprises the low- southwestern-most edge of the Conasauga Riv- est unit of the global Paibian Stage (Gradstein er Valley. and others, 2005; Babcock and Peng, 2007), The Conasauga Formation in northwestern which is penecontemporaneous with the Lau- Georgia spans much of the Middle Cambrian rentian Steptoean Stage (Ludvigsen and We- (Schwimmer, 1989, Schwimmer and Montante, strop, 1985; Peng and others, 2004). The new 2007) through the lowermost Upper Cambrian Conasauga sites include three agnostoid species (Figure 1b). Collections for this report are from common to the Glyptagnostus reticulatus Zone exposures in the upper portion of the Conasau- (Peng and Robison, 2000), including G. reticu- ga Formation in Georgia. The Conasauga in its latus itself. Therefore, these Conasauga sites in- entire geographic range, extends down to the clude age-specific genera and species base of the Middle Cambrian, up through most incorporated in both Laurentian polymeroid- of the Upper Cambrian, and is mapped from and global agnostoid trilobite chronostrati- central Alabama, across northwestern Georgia, graphic zone concepts. to eastern Tennessee and southwestern Virginia (Palmer, 1971; Hasson and Hasse, 1988; Os- SYSTEMATIC PALEONTOLOGY borne and others, 2000), reaching local thick- nesses exceeding 1000 m. Across the entire Repository and Terminology exposure, the Conasauga represents multiple depositional environments forming on the ma- Specimens described and figured are curated rine shelf and in shelf-edge basins along the sa- and housed in the Cambrian Research collec- lients and recesses of the Laurentian margin of tions (CSU ) of Columbus State University, the Cambrian Iapetus Ocean. These paleoenvi- Columbus, Georgia. Descriptions of ronments include shallow-water peritidal clas- polymeroid trilobites follow Whittington tic wedges, admixed outer shelf carbonates and (1997a); agnostoid morphology also incorpo- shales, and algal carbonate shoals on the shelf- rates basic terminology from Öpik, 1967, as to-basin boundaries (Hasson and Haase, 1988). modified by Whittington and Kelly, 1997, and Peng and Robison, 2000. To protect fragile fossil sites, only general localities are given here and in Figure 1a: precise locality coordinates are available for qualified research by contact with the first author.

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Order Agnostida Salter, 1864 individual; CSU -07-4-9, CSU -07-4-11, ce- Subfamily Agnostinae M’Coy, 1849 phala; and CSU -07-4-10, CSU -07-4-12, Agnostus Brongniart, 1822 pygidia. Agnostus inexpectans Kobayashi, 1938 Occurrence—Locality 1, Murray County, Figure 2.1 Georgia. Diagnosis—Cephala with sagittally short gla- Referred Material— CSU -07-4-1, a com- bella, edges slightly swollen at M3, genae with plete exoskeleton, part and counterpart; irregular, radial scrobiculae with moderately CSU -07-4-2, an incomplete cephalon. deep furrows, preglabellar medial furrow may Occurrence— Locality 1, Murray County, be poorly distinct because of cross furrows. Py- Georgia (see Figure 1a). gidium with elevated, spinose axial nodes, Diagnosis—Cephala with moderate to deep slightly to moderately scrobiculate pleurae, F1 median preglabellar furrow, transglabellar fur- slightly constricted at lateral edges but not sub- row relatively shallow, glabellar furrows F1 and tending distinct M1. F2 well-incised, subtending distinct M2 and Discussion—Aspidagnostus is an easily recog- M3. Pygidium slightly expanded posteriorly, nizable, biostratigraphically-useful genus be- posteroaxis not touching border furrow, F1 con- cause of the unique pygidial medial spine. The tinuous across pygidial axis, F2 weakly demar- specimens here are very small and poorly pre- cated around axial node. served, but nevertheless readily identifiable to Discussion—Peng and Robison (2000) provd- genus and species. ed a complete review of this genus and species, This species was first identified by Palmer, including its various reassignments between In- 1962, in the Conasauga Formation at Cedar nitagnostus and Agnostus. The agnostoids in Bluff Alabama, in addition to localities in the the sites to be discussed here tend to be poorly Great Basin. Subsequently it is has been recog- preserved at the microscopic level, and also nized nearly globally, co-occurring with other tend to split from the enclosing matrix with the agnostoids of the Glyptagnostus reticulatus exoskeleton adhering to one part of the sedi- Zone. Pratt (1992) noted that Aspidagnostus ru- ment, and the internal cast on the counterpart. gosus occurs in the lowest Steptoean to latest The complete individual of Agnostus inex- Marjuman strata. Therefore, we assume that the pectans figured here (Figure 2.1) has the better assemblage in study may be likewise con- preservation on the internal cast. strained to the very oldest portion of the G. re- The specimen figured here, although poorly ticulatus biozone. preserved, shows the characteristic cephalic and pygidial furrows and lobation. Palmer (1962) Family Indeterminate reported specimens of A. inexpectans from the Subfamily Glyptagnostinae Conasauga Formation in Cedar Bluff, Alabama, Whitehouse, 1936 located approximately 80 km west of the local- Genus Glyptagnostus Whitehouse, 1936 ity discussed here. Agnostus inexpectans is Glyptagnostus reticulatus (Angelin, among the most cosmopolitan of Asian, Austra- 1851) lian and Laurentian Upper Cambrian agnos- Figures 2.5-2.8 toids. Referred Material—CSU -07-4-3, CSU - Family Clavagnostidae Howell, 1937 07-4-5, CSU -07-4-7 pygidia; CSU -07-4-4, Genus Aspidagnostus Whitehouse. CSU -07-4-6, cephala; plus numerous addi- 1936 tional specimens. Aspidagnostus rugosus Palmer, 1962 Occurrence—Locality 1, Murray County, Figures 2.2-2.4 Georgia Diagnosis—Complexly scrobiculate agnos- Referred Material— CSU -07-4-8, complete toids with narrow border furrows, cephalon

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Figure 2—Agnostoid trilobites from Locality 1. 1, Agnostus inexpectans Kobayashi, internal cast of complete individual, CSU -07-4-1, x18. 2-4, Aspidagnostus rugosus Palmer. 2, complete individual, CSU -07-4-8, x16; 3, cephalon, CSU -07-4-9, 4, external mold of pygidium, CSU -07-4-10, both x20. 5-8, Glyptagnostus reticulatus (Angelin). 5-6 cephala, CSU -07-4- 4, x17, CSU 07-4-6, x15; 7-8, pygidia CSU -07-4-3, CSU -07-4-5, both x15.

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with subquadrate anteroglabella, median preg- Order Ptychopariida Swinnerton, 1915 labellar furrow present, basal lobes elongate. Suborder Ptychopariina Richter, 1933 Pygidium with tapering axis constricted at M2, Family Pterocephaliidae Kobayashi, not touching border furrow, posterior median 1935 furrow present. In some specimens the pattern Subfamily Aphelaspinae Palmer, 1960 of rugae is multi-order, forming a nodulose pat- Genus Aphelaspis Resser, 1935 tern. Aphelaspis brachyphasis Palmer, 1962 Discussion—This is arguably the most distinc- Figures 3.1-3.7 tive and recognizable agnostoid genus known because of the elaborate and specifically vari- Referred Material— CSU -07-2-1, CSU - able scrobiculation on cephala and pygidia. The 07-5-5, complete holaspides with intact genus has been discussed exhaustively through librigenae; CSU -07-5-6, larger holaspis with one and one-half centuries of literature, and of- intact librigenae, missing posterior segments ten split into multiple species and subspecies and pygidium; CSU -07-2-3, cephalon expos- based on the variable patterns of furrows (Sher- ing ventral sclerites; CSU -07-2-4, partial gold, 1982; Pratt, 1992; Peng and Robison, late-stage meraspis missing pygidium; CSU - 2000). Species of Glyptagnostus are particular- 07-2-7, CSU -07-2-8, pygidia. ly useful, globally distributed guide fossils, and Occurrence—Locality 1, Murray County, comprise two biozones in the Late-Middle to Georgia. early-late Cambrian, of which the specimens Diagnosis—Ptychopariina with co-equal preg- here denote the younger biozone. It is signifi- labellar field and border, librigenae separated cant to biogeographic implications of the Cona- by a narrow rostral plate, natant hypostome sauga fauna in study (in discussion to follow) clearly detached skeletally from the doublure, that Pratt (1992) noted (p. 87): “…species of short preglabellar field with indistinct border Glyptagnostus are distributed in slope and furrow; short, stout genal spines reaching poste- deeper shelf lithofacies….” riorly no farther than the second thoracic seg- Resser (1938) and Palmer (1962) described ment and laterally extending from the thorax at specimens of Glyptagnostus from the Conasau- relatively large angles. Pygidia relatively wider ga Formation at Cedar Bluff, Alabama, located (tr.) than long, with three poorly demarcated ax- approximately 100 km southwest of the site of ial rings plus indistinct posteroaxis. specimens here. Because these had relatively Discussion—This Aphelaspis species is ex- less intensely scrobiculate pygidia, Resser re- traordinarily abundant in Locality 1 and com- ferred the Conasauga Formation specimens to a monly preserved with intact librigenae and new species, G. angelini, which Palmer (1962) found in a wide variety of size classes, includ- revised as a subspecies, G. reticulatus angelini. ing meraspides. Many species of Aphelaspis Subsequent authors (Pratt, 1992; Peng and have been recognized, many of which are dubi- Robison, 2000) have observed that the intensity ous: over-splitting of the genus is evident in of scrobiculation varies both ontogenetically various literature sources: for example, Rasetti and temporally in the Glyptagnostus reticulatus (1965) recognized fifteen species of Aphelaspis clade, with geologically older and more juve- in Tennessee, including eleven of which he nile individuals less ornamented. Therefore, it erected in that single publication. Among the is currently accepted that G. reticulatus com- many (and variable) described species of prises a single variable species with an apparent Aphelaspis, the broad, strongly divergent spines cline in complexity of ornamentation that may combined with the short, indistinctly segmented be useful to delimit the stratigraphic age of pygidium closely conform with the type speci- specimens. The specimens illustrated here (Fig- mens from Nevada in Palmer (1962), as well as ures 2.5-2.8) are mature individuals that show material tentatively referred in Pratt (1992). the average intensity of furrows for the strati- The specimens from the Conasauga Formation graphically older representatives of the species. are flattened but complete, and therefore some

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Figure 3—Ptychopariine trilobites from Localities 1 and 2. 1-7, Aphelaspis brachyphasis Palmer, from Locality 1; 1, 2, larger holaspides with attached librigenae, showing iron-oxide halos; 1, CSU -07-2-1, 2, CSU -O7-5-6, both x5.5; 3, ventral view of cephalon, showing labrum and rostral plate, CSU -07-2-3, x7.5; 4, small holaspis with attached librigenae, CSU -07-5-5, x5; 5, partial meraspis, CSU -07-2-4, x10; 6,7, pygidia; 6, CSU -07-2-7, x3.5; 7, CSU -07-2-8, x5. 8-10, Eugonocare (Olenaspella) separatum (Palmer), from Locality 2; 8, holaspis with intact librigenae, CSU -07-3-1, x3.5; 9, cephalon and anterior thorax of larger individual, CSU -07-3-5; 10, isolated librigena, CSU -07-3-6, both x2.

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features comparable with the holotype may be mens discussed here clearly conform to that exaggerated or distorted, such as the lateral morphology, whether or not the subgeneric spread of the genal spines and the width of the classification is necessary. pygidium. This is the first occurrence of this species in the eastern continent. TAPHONOMY AND BIOGEOGRAPHY Genus Eugonocare Whitehouse, 1939 Eugonocare (Olenaspella) separatum Preservation of Complete (Palmer, 1962) Aphelaspis and Eugonocare Figures 3.8-3.10 Specimens of Aphelaspis and Eugonocare Referred Material—CSU -07-3-1, complete from both localities contain a majority of indi- holaspis; CSU -07-3-4, larger cephalon and viduals with intact librigenae (see, for example, partial thorax; CSU -07-3-5, isolated librige- Figures 3.1-3.4, 3.8, 3.9). Such fossils represent na. dead trilobites rather than molted exuviae, since Occurrence—Locality 2, Gordon County, the librigenae of ptychopariines were typically Georgia. separated during exuviation along the facial su- Diagnosis—Aphelaspinae with transversely tures (Whittington, 1997b), and are almost al- wide cranidia, equally wide librigenae with ways found in molts separated from the broad margin, wide, deep, marginal furrow. cranidia. At locality 1 complete Aphelaspis in- Preglabellar field long (sag.), slightly inflated, dividuals are very abundant and frequently oc- with fine radiating striations. Genal spines long cur as multiples, sometimes overlapping, within and broad, reaching posteriorly to the sixth tho- decimeter-scale slabs. Such occurrences are racic segment. Thoracic segments with deep in- termed “body clusters” in Whittington, 1997b, terpleural furrows, terminating in relatively and represent death assemblages (versus “molt long marginal spines. Pygidium relatively small clusters” representing marine current sorted ex- with five segments and a single pair of marginal uviae accumulations). Given the abundance of spines on the anterior segment. apparently dead individuals, combined with the Discussion—The specimens here retain the well sorted, fine-grained enclosing lithology, it librigenae, showing the proportionately large is inferred that the Aphelaspis specimens here size of the cephala. However, the preservation were killed and preserved by episodes of rapid of some individuals incorporates distortion of immuration in mudflows, most likely on the the claystone matrix (e.g. Figure 3.9), skewing outer marine shelf or a deeper marine basin en- the body proportions. Most generic and specific vironment. descriptions of Eugonocare sp. are based on It is also significant that many of the com- isolated cranidia, free cheeks and pygidia, and plete (thus dead) specimens are surrounded by complete individuals such as figured here are iron oxide (goethite) halos (see, e.g., Figure relatively rare. It is therefore notable that the 2.1). These oxides are the final event in a pres- thorax shows segments with deep interpleural ervational-depositional sequence (Schwimmer furrows and elongate marginal spines. The mar- and Montante, 2007) which begins with precip- ginal spines, in particular, are confluent with the itation of pyrite around the decaying organism diagnostically spinose morphology of the ante- (Borkow and Babcock, 2003; Popa and others, rior pygidium. Identification of Eugonocare 2004). Pyrite is commonly precipitated when separatum in the Conasauga Formation further decay gases cause locally reducing conditions extends the geographic range to eastern North in iron and sulfur-rich marine waters, which America. Peng (1992) recognized three subgen- subsequently oxidizes to ferrous oxides when era of Eugonocare, including Eugonocare (Ole- the sediment is exposed at any later time to naspella), which in his concept comprises a higher oxygenated groundwater or subaerial en- distinct North American subgenus. The speci- vironments. In addition to authigenic sulfide

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deposition, we infer there was locally low oxy- Valley, Georgia, assemblages have identical ag- gen conditions in the Conasauga Formation nostoids, but that the abundant Aphelaspis based on the near absence of burrow traces in brachyphasis of the Conasauga Valley were not the Conasauga Valley mudstones containing the reported at Cedar Bluff (Palmer, 1962). The complete Aphelaspis specimens: the absence of muddy, low-oxygen sedimentary and tapho- significant infaunal traces implies low oxygen nomic conditions inferred for the Conasauga conditions especially below the sediment-water Valley localities, suggest that these deposits ac- interface. cumulated on the distal edge of the shelf or in a Similar pyrite deposition and goethite re- relatively deep intrashelf basin. In contrast, placement around intact trilobite specimens Palmer (1962) reported the strata at Cedar was reported in nearby late Middle Cambrian Bluff, Alabama (located northwestward, to- trilobite assemblages (Bolaspidella Zone) in the ward the mid-continent) to be composed of in- Coosa Valley in Georgia (Schwimmer and terbedded shales and thin-bedded limestones. Montante, 2007). In both the latter and present This slight sedimentary and faunal change from situations, the mode of trilobite preservation west (Cedar Bluff, Alabama) to east (Conasau- (intact librigenae and oxides halos) apparently ga Valley), may reflect the paleotopographic resulted from the combination of relatively low- break (Thomas and others, 2000) from the Ala- oxygen conditions below the sediment-water bama Promontory shelf edge (then, due north- interface, and well-sorted mud sedimentation west) across the transform to deeper water in on the outer marine shelf. These similar marine the Tennessee Embayment (then, to the south- conditions, found in two closely-spaced trilo- east). Carrying this argument one step further, bite chronozones (Bolaspidella and Aphelaspis we may also infer that the species Aphelapsis Zones) suggest that stable marine conditions brachyphasis, which was apparently absent at persisted on the extreme southwestern conti- Cedar Bluff, may have been endemic to the nental shelf-edge. deeper, basinal marine environment represent- ed in the Conasauga Valley localities. Paleobiogeography ACKNOWLEDGMENTS The Conasauga River Valley localities discussed here are the southeastern most exposures We are indebted to Roxy Warren for sharing of Upper Cambrian strata in the southern Appa- the key agnostoid specimens, and for field as- lachian region. The nearest Upper Cambrian tri- sistance. We are also grateful to Allison R. lobite faunal locality (which correlates very Palmer for initial guidance to frame the project, well biostratigraphically with the Conasauga to Brian R. Pratt for sharing important data re- Valley localities) is at Cedar Bluff, Alabama, in sources, and to Clinton I. Barineau for advice the Coosa River Valley (Palmer, 1962; Butts, on regional palinspastic reconstruction. Assis- 1926), located approximately 75 km to the tance in preparing figures was supplied by Tra- west. The palinspastically reconstructed dis- cy L. Hall and Roger Brown. We also tance between these localities was substantially appreciate valuable critical review and com- greater in the Cambrian, and also involves some ments by Tin-Wai Ng. clockwise rotation (Thomas and Bayona, 2005) since there are several transform detachments and thrust fault zones intervening between the REFERENCES localities. The Late Cambrian separation between these Aphelaspis faunal sites reconstructs Angelin, N. P., 1851, Palaeontologia scandinavica, Pars 1, Crustacea formationis transitionis: Holmiae, Stock- to approximately 145 km on the Cambrian ma- holm, 24 p. rine shelf. Babcock, L. E., and Peng, S. C., 2007, Cambrian chronos- It is noteworthy in this context that the re- tratigraphy: Current state and future plans: Palaeogeog- spective Cedar Bluff, Alabama, and Conasauga raphy, Palaeoclimatology, Palaeoecology, 254: 62-66.

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Babcock, L. E., Peng, S. C. Geyer, G. and Shergold J. H., derberg Shale, Eureka District, Nevada: United States 2005, Changing perspectives on Cambrian chronos- Geological Survey, Professional Paper, 334-C, 109 p. tratigraphy and progress toward subdivision of the Palmer, A. R., 1962, Glyptagnostus and associated trilobites Cambrian System: Geosciences Journal, 9:101-106. in the United States: United States Geological Survey Borkow, P. S. and Babcock, L. E., 2003, Turning pyrite con- Professional Paper 374-F, 49p., 6 pl. cretions outside-in: role of biofilms in pyritization of Palmer, A. R., 1965, Trilobites of the Late Cambrian Ptero- fossils: Sedimentary Record. 1:4-7. cephaliid Biomere in the Great Basin, United States: Brongniart, A. 1822, Les trilobites, p. 1-65, in A. Brongniart United States Geological Survey Professional Paper and A.-G. Desmarest, Histoire naturelle des crustacés 493, 100 p. fossiles, sous les rapports zoölogiques et géologiques. Palmer, A. R., 1971, Cambrian of the Appalachian and east- F.-G. Lavrault, Paris. ern New England regions, eastern United States, Butts, C., 1926, The Paleozoic rocks: Geological Survey of p.169-217: in C. H. Holland (ed.) Cambrian of the New Alabama, Special Report, 14:41-230. World: Wiley Interscience, New York. Gradstein, F. M., Ogg J. G. and Smith, A. G., 2005, A geo- Peng, S. 1992. Upper Cambrian biostratigraphy and trilobite logic time scale, 2004: Cambridge University Press, faunas of the Cili-Taoyuan area, northwestern Hunan, 163 p. China: Association of Australasian Paleontologists, Hasson, K. O. and Haase, S., 1988, Lithofacies and paleo- Memoir 13, 119 p. geography of the Conasauga Group (Middle and Late Peng, S. and Robison, R. A., 2000, Agnostid biostratigraphy Cambrian) in the Valley and Ridge Province of east across the Middle-Upper Cambrian boundary in Hunan, Tennessee: Geological Society of America Bulletin, China: Journal of Paleontology, Memoir, 53, 104 p. 100: 234-246. Popa, R., Kindle, B. and Badescue, A., 2004, Pyrite fram- Howell, B. F., 1937, Cambrian Centropleura vermontensis boids as biomarkers for iron-sulfur systems: Geomicro- fauna of northwestern Vermont: Geological Society of biology Journal, 21:193-206. America Bulletin, 48: 1147-1210. Pratt, B. R., 1992, Trilobites of the Marjuman and Steptoean Kobayashi, T., 1935, The Cambro-Ordovician formations stages (Upper Cambrian), Rabbitkettle Formation, and faunas of South Chosen. Palaeontology. Part III. southern Mackenzie Mountains, northwest Canada: Cambrian faunas of South Chosen with a special study Palaeontographica Canadiana, 9, 179 p. on the Cambrian trilobite genera and families: Journal Rasetti, F., 1965, Upper Cambrian trilobite faunas of north- of the Faculty of Science, Imperial University of Tokyo, eastern Tennessee: Smithsonian Miscellaneous Collec- sec. II, 4:49-344. tions, 148(3), 127 p., 21 pl. Kobayashi, T., 1938, Upper Cambrian trilobites from British Resser, C. E., 1935, Nomenclature of some Cambrian trilo- Columbia, with a discussion on the isolated occurrence bites: Smithsonian Miscellaneous Collections, 93, 46 p. of the so-called “Olenus” beds of Mount Jubilee: Japa- Resser, C. E., 1938. Cambrian System (restricted) of the nese Journal of Geology and Geography, 15:149-192. southern Appalachians: Geological Society of America Ludvigsen, R. And Westrop, S. R., 1985, Three new Upper Special Paper 15, 140p. Cambrian stages for North America: Geology, 13:139- Richter, R., 1933, Crustacea: Handwörterbuch der Natur- 143. wisenschaften (2nd ed.), 2, Jena:840-864. M’Coy, F., 1849, On the classification of some British fossil Salter, J. W., 1864, A monograph of British trilobites, Pt. 1: Crustacea with notices of some new forms in the Uni- Palaeontographical Society, London. Monograph, vol- versity collections at Cambridge: Annals and Magazine ume for 1862:1-80. of Natural History (series 2), 4:161-179, 330-335, 393- Schwimmer, D. R., 1989, Taxonomy and biostratigraphic 414. significance of some Middle Cambrian trilobites from Ogg, G., 2009, Global boundary stratotype sections and the Conasauga Formation in western Georgia: Journal points (GSSP): International Commission on Stratigra- of Paleontology, 63:484-494. phy: http://stratigraphy.science.purdue.edu/ Schwimmer, D. R. and Montante, W. M., 2007, Exceptional gssp/. fossil preservation in the Conasauga Formation, Cam- Öpik, A. A., 1967, The Mindyallan fauna of north-western brian, Northwestern Georgia USA: Palaios, 22:360- Queensland: Australia Bureau of Mineral Resources, 372. Geology and Geophysics Bulletin, 74, 404p. (vol. 1), Shergold, J. H., 1982, Idamean (Late Cambrian) trilobites, 176 p. (vol. 2). Burke River structural belt, Western Queensland: Osborne, W. E., Thomas, W. A., Astini, R. A. and. Irvin, G. Bureau of Mineral Resources, Geology and Geophys- D., 2000, Stratigraphy of the Conasauga Formation and ics, Bulletin 187, Australian Government Publishing equivalent units, Appalachian thrust belt in Alabama, p. Service, 69 p. 1-17: in Osborne and others (eds.), The Conasauga For- Swinnerton, H. H., 1915, Suggestions for a revised classifi- mation and equivalent units in the Appalachian Thrust cation of trilobites: Geological Magazine, new series, Belt in Alabama: Alabama Geological Society, 37th 2:407-496, 538-545. Annual Field Trip Guidebook, 100 p. Thomas, W. and Bayona, G., 2005, The Appalachian thrust Palmer, A. R., 1960, Trilobites of the Upper Cambrian Dun- belt in Alabama and Georgia: Thrust-belt structure,

40 Schwimmer.fm Page 41 Monday, June 18, 2012 11:54 AM

UPPER CAMBRIAN TRILOBITES, NORTH GEORGIA

basement structure, and palinspastic reconstruction: Geological Survey of Alabama Monograph 16, 48 p. Thomas, W.A., Astini, R. A., Osborne, W. E., and Bayona, G., 2000, Tectonic framework of deposition in the Con- asauga Formation, p. 19-40: in Osborne and others (eds.), The Conasauga Formation and equivalent units in the Appalachian Thrust Belt in Alabama: Alabama Geological Society, 37th Annual Field Trip Guidebook. Walcott, C. D., 1916a, Cambrian geology and paleontology III, No. 3--Cambrian trilobites: Smithsonian Miscella- neous Collections 64(3):155-283. Walcott, C. D., 1916b, Cambrian geology and paleontology III, No. 5--Cambrian trilobites: Smithsonian Miscella- neous Collections 64(5):303-451. Whitehouse, F. W., 1936, The Cambrian faunas of north- eastern Australia, Pt. 1, stratigraphic outline, Pt. 2, Tri- lobita (Miomeria): Memoirs of the Queensland Museum, 11:59-112. Whitehouse, F. W., 1939, The Cambrian faunas of north- eastern Australia, part 3: the polymerid trilobites: Mem- oirs of the Queensland Museum, 40:179-282. Whittington, H. B., 1997a, Morphology of the exoskeleton, p. 1-84: in R. L. Kaesler (ed.),Treatise on Invertebrate Paleontology, Part O, Arthropoda I: Trilobita (Revised), Volume 1. The Geological Society of Amer- ica and the University of Kansas Press, Lawrence. Whittington, H. B., 1997b, Mode of life, habitats, and occurrence, p. 137-169: in R. L. Kaesler (ed.), Treatise on Invertebrate Paleontology, Part O, Arthropoda I: Trilo- bita (Revised), Volume 1. The Geological Society of America and the University of Kansas Press, Lawrence. Whittington, H. B. and Kelly, S. R. A., 1997. Morphological terms applied to Trilobita, p. 313-329: in R. L. Kaesler (ed.), Treatise on Invertebrate Paleontology, Part O, Arthropoda I: Trilobita (Revised), Volume 1. The Geo- logical Society of America and the University of Kan- sas Press, Lawrence.